The present invention relates to a threat detection apparatus and a threat detection method, and in particular to a threat detection apparatus and a threat detection method using X-rays.
As for reference relating to the present invention, a threat detection apparatus that radiates X rays having two energy levels alternately is described in JP-A-2001-235434. A threat detection apparatus using a combination of scan projection and CT (Computed Tomography) is described in U.S. Pat. No. 5,182,764. In addition, a threat detection apparatus using a combination of scan projection and X-ray tubes (two tubes) differing in energy is described in U.S. Pat. No. 5,367,552.
These threat detection apparatus utilize large-sized X-ray CTs of high speed. The threat detection apparatus can also detect explosives that are hard to detect in inspection apparatus using X-ray transmission seen in airports in Japan, and they are used mainly in large-sized airports in United States. However, these apparatus are as heavy as 3 tons to 7 tons, and hard to move. Therefore, the degree of freedom in layout cannot be obtained. The reasons why these apparatus become large in size and mass are as follows: (1) Since a CT image is obtained with continuous rotation, the structure of slip rings becomes complicated. (2) A high output X-ray tube and a high voltage power supply (HVPS) are needed so that an X-ray is not absorbed by a conveyor belt even if the X-ray is incident on the conveyor belt at a shallow angle in order to pick up a CT image on the conveyor belt.
For small-sized airports such as Narita and Haneda, a threat detection apparatus that is small in apparatus size, small in mass, low in price, and high in precision is needed. For that purpose, it is necessary to solve the problems of (1) and (2).
Since threat detection apparatus are operated every day, a threat detection apparatus that is long in life and small in the number of times of maintenance is also needed.